How are conjugation endings (たい, た, ない) called by Japanese linguists*?

Examples: 食べた tabeta 'ate', 食べない tabenai 'do not eat'

According to Wikipedia, and an electronic dictionary, it seems they are considered 助動詞 jodōshi.

I still wonder if they are not classified as other parts of speech (for instance 助詞 joshi), or if they are considered suffixes (接尾辞 setsubiji).

It would be possible that they are directly referred as 活用形 katsuyōkei.

*By "Japanese linguists" I mean linguists who are Japanese, working in Japan, and producing textbooks such as those studied in schools; or scientific research published in Japanese, in Japanese journals.

  • 1
    In the first place, I wouldn't regard たい/た/ない as conjugation endings. I think it's better you include fully conjugated words (and maybe English counterparts) to clarify which part of words you are referring to. Related complimentarily: Conflicting Definitions of Verb “Roots,” “Bases,” and “Stems”
    – sundowner
    Nov 6, 2023 at 11:01
  • @sundowner Thx, I edited my question
    – Starckman
    Nov 6, 2023 at 12:11
  • I deleted my previous answer and made a new post. I hope the new one answers your problem.
    – naruto
    Nov 6, 2023 at 13:39

2 Answers 2


You have answered your own question, but (食べ)たい, (食べ)ない, (食べ), (食べ)ます and so on are almost always called 助動詞 in traditional 国文法 studied by 国語学者/日本語学者* and taught by Japanese middle/high school teachers. These are always called 助動詞 in monolingual dictionaries, too. Importantly, these are words on their own, and not part of a verb's conjugation form.

(* I personally hesitate to call them 言語学者 for a reason, but I won't go into the details about it...)

For example, 書かない consists of two words, 書か (未然形 of 書く) + ない (助動詞 for negation). 書きたい is also two words, 書き (連用形 of 書く) + たい (助動詞 for desire). 書いた is 書い (another 連用形 of 書く) + (助動詞 for past tense). 書きたくなかった has all the four words, 書き (連用形 of 書く) + たく (未然形 of たい) + なかっ (連用形 of ない) + (終止形 of た).

This is different from what you may have learned as a JSL (Japanese-as-a-second-language) learner, but that's how the Japanese grammar is usually taught and discussed in Japanese.

It would be possible that they are directly referred as 活用形 katsuyōkei.

Indeed, if you're seeing only simple examples like 歩い, it may be hard to see how it's different from "walked". The main reason these 助動詞 are considered independent words is that they can be combined to say complex things.

For example, 食べさせられたくなかった means "did-not-want-to-be-made-to-eat", but it's odd to call something like this a "form" when it can be logically split into smaller parts. According to 国文法, this is a "simple" combination of 6 words, 5 of which are 助動詞: 食べ + させ (causation) + られ (passive) + たく (desire) + なかっ (negation) + (past).

書きませんでした is often introduced as a "form" (negative-polite-past-form) in JSL textbooks, but this is just for the sake of convenience. The rules governing 助動詞 are a little too tricky for a beginner, so it's faster to learn them by rote as a form at first.

For another thing, while there are a few irregular verbs in Japanese, their irregularity does not cross word boundaries and affect the following 助動詞. For example, 行く is a well-known irregular verb whose "past form" is not 行いた but 行った, but you can see the た part remains た. This is another reason why 助動詞 are considered separate. In English, the past form of go is went, and it's impossible to see two words in it.

I still wonder if they are not classified as other parts of speech (for instance 助詞 joshi), or if they are considered suffixes (接尾辞 setsubiji).

助動詞 are clearly different from 助詞 (particles; を, が, へ, から, etc):

  • 助詞 usually follow 体言 (nouns), whereas 助動詞 usually follow 用言 (verbs and i-adjectives).
  • 助詞 never conjugate, whereas 助動詞 can conjugate by themselves. For example, たい and ない themselves conjugate like an ordinary i-adjective (たく, たかっ, たけれ; なく, なかっ, なけれ), allowing another 助動詞 to follow it.
  • In terms of purpose, 助詞 is closer to English prepositions (to, of, at, etc) while 助動詞 is closer to English auxiliary verbs (can, should, must, etc).

A 接尾辞 (suffix) forms another single word. For example, in English, "boys" is still one word, and "brighten" is still one word. However, a Japanese 助動詞 is a bit too flexible to be called a part of a word, as described above, and that's why they are not called suffixes.


(EDIT: Oh, I noticed 接尾辞 in Japanese Wikipedia does not agree with what I explained above. So this is one way where 国文法 and 言語学 differ... Whoever wrote this seems to think even が and は are suffixes based on some linguistic theory, but I don't think those who adhere to 国文法 would agree.)

  • 3
    Phonologically, 助詞 are clitics. But then, so are English words like a, an, and the. Phonological clitic-ness and grammatical / syntactical word-ness are separate analyses: belonging to one category does not necessarily say much about membership in the other category. Nov 6, 2023 at 19:39
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    How does traditional 国文法 explain that "past form" た becomes だ for verbs such as よぶ, よむ, しぬ? (By the way, English went is originally from separate verb wend).
    – Arfrever
    Nov 7, 2023 at 7:49
  • 1
    @Arfrever A dictionary entry for た usually has a usage note like "ガ・ナ・バ・マ行の五段動詞に付くときは濁音化する". I tend to think they're two forms of the same word, but I'm not sure. It's perhaps the same as asking whether a and an are different words in English.
    – naruto
    Nov 7, 2023 at 8:06
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    @EiríkrÚtlendi I know how it developed historically. I consider this -ta (and its -da variant) to be suffix rather than separate word. You might also be interested in knowing that in LMJ times, -b and -m verbs developed 2 variants of onbin stems, with -u (which is merged with preceding vowel to create long vowel) and with -n. E.g. both yob- and yom- had form youde /joːde/ ~ yonde. (Bjarke Frellesvig 2010 "A History of the Japanese Language", page 347)
    – Arfrever
    Nov 7, 2023 at 20:22
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    @Arfrever But your argument does not mean 国文法 is broken or inconsistent by itself, right? 国文法 is the result of research from the Edo period, and they of course didn't consider how to explain the grammar of Latin and Japanese consistently. For many 日本語学者, consistency with Japan's past research is more important than consistency with Latin, and there is little motivation to change the definition of suffix.
    – naruto
    Nov 9, 2023 at 3:01

A conjugation ending is usually called 活用語尾, which is a morpheme (形態素) dependent to a word, unlike independent ones like a noun and a verb. Whether it's part of a word or attached to a word/stem can be debatable, though.

I don't think the endings can be called 活用形 (katsuyōkei), because the name usually refers to conjugated forms (= stem + ending), and thus creates confusion.

As for た, たい and ない, they are usually called 助詞 (when it doesn't conjugate by itself) and 助動詞 (when it conjugates). Both are separate from conjugation endings. I think one difference between conjugation endings and non-conjugation endings would be that the latter can be written more clearly and consistently separate from the verb.

Here is a material provided by Bunkacho where they use 活用語尾: https://www.bunka.go.jp/kokugo_nihongo/sisaku/joho/joho/kakuki/04/bukai02/02.html

A Japanese language 101 lecture by the OUJ uses 活用語尾: https://v.ouj.ac.jp/view/ouj/#/navi/player?co=30117&ct=V&ca=30012 (around 25:00-30:00). It also discusses (non-traditional) analysis of verbs like 書かない → 書k + aない where aない is a 活用語尾. This makes more sense linguistically, but it doesn't sit well with the Japanese orthography where "k" and "a" would seem merged into one indivisible unit as か or カ.

  • I think that traditional orthography (for any language) is better ignored for discussions of real grammar... -(a)nai developed somehow, probably by analogy to independent adjective nai (無い), but negation suffix actually reconstructed for Old Japanese or earlier Proto-Japonic, is -an-, e.g. in kak-an-u (where -u is conclusive/terminal suffix). But even in much later history of Japanese we have evidence of boundaries within single kana, e.g. complex copula de-ar-u (である) → de-a (であ) → d-a (だ) (I am not advocating for romanization of だ as d-a or d a).
    – Arfrever
    Nov 9, 2023 at 0:32

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